Oligovillous cells of the epidermis: sensory elements of lamprey skin

The epidermis cf Lampetra spp. contains several kinds of differentiated cell; one innervated variety is characterized by bearing a group of large apical microvilli which project from the surface of the skin. In Lampetra planeri such oligovillous cells are numerous under the oral hood of the ammocoete larva, on the papillae fringing the dorsal fin and bordering the gill vents of the adult, and at the tip of the male genital papilla. Elsewhere on the head, body and fins they are present but more scattered, which appears to be the condition also in adult anadromous Lampetra fluviatilis . There are differences in the number and dimensions of the microvilli found on oligovillous cells, but each is supported by a stout core of actin filaments extending a variable distance down into the cytoplasm. Under the apex of the cell there are microtubules and numerous vesicles which are thought to be concerned in the renewal of the membrane on the microvilli. Beside and proximal to the nucleus is a system of channels of rough endoplasmic reticulum, and a stack of membranous cisternae which appears to have been derived from the endoplasmic reticulum. A nerve fibre is associated with the base of the cell which is indented by a spur-like process from the neurite. Typical "synaptic vesicles" are not found in the cell but irregular vesicular or canalicular profiles are associated with the cell membrane adjoining the neurite spur. The space between the cell and neurite membranes contains extracellular material with a characteristic appearance of prickle-like densities on the cell side meeting densities on the neurite membrane. Variations in the cytology of oligovillous cells can be explained in terms of a cycle of development and de-differentiation. Certain cells with vesicles throughout the cytoplasm and with a narrow apex without microvilli are interpreted as degenerate examples. The oligovillous cells are thought to be chemosensory receptors.     

Multivillous cells: epidermal sensory cells of unknown function in lamprey skin

In Lampetra planeri the epidermis of adult and ammocoete contains a type of bipolar cell, with numerous microvilli about 1 μm long on the apex, and the base associated with a nerve fibre by bar-type synapses. These multivillous cells can be identified with types found by previous authors. In the ammocoete, they correspond to those previously described as epidermal photoreceptors, which were shown to be innervated from the lateralis nerves; this is consistent with the mode of innervation seen by electron microscopy. A pigment seen in the photoreceptors is presumably represented by an organelle consisting of a tangle of microcylinders or tubules, associated in tetrads. The organelle can be called a sinnet, from its configuration. In adult skin, multivillous cells have a close resemblance to the receptor cells of the end buds of adult lamprey epidermis, but they are not associated with supporting cells.     

Characterization of label-retaining cells in the epidermis of a human skin equivalent

Abstract. The human skin equivalent (HSE) is an in vitro reconstructed model that resembles skin morphologically and biochemically. The HSE is formed by overlaying a fibroblast-populated collagen matrix with a suspension of epidermal cells. Basal keratinocytes attach to the dermal equivalent via a newly formed basement membrane and multiply to form a stratified, differentiated epidermis. The aim of the studies described here was to characterize the basal cells of the HSE in terms of their cell cycling potential. The experiments utilized long-term labelling of the cells with tritiated thymidine ([³H]dT), followed by irradiation with ultraviolet light. [³H]dT incorporation was analysed via routine autoradiography. Irradiation with 100 J/m² UV light increased the number of labelled basal cells by 58% over the control, the maximal stimulation observed. Decreased numbers of labelled basal cells were observed at doses of UV light greater than 100 J/m². The maximal number of labelled basal cells was observed on day 14 and decreased over time; the number of labelled suprabasal cells increased concomitantly. Label-retaining cells (12%) persisted in the stratum basale of control HSEs after 32 days in culture. Labelled cells were observed in the apical layers of the stratum granulosum of control HSEs after 22 days in culture. These data suggest that the stratum basale of the HSE contains a population of slow-cycling cells whose characteristics resemble a subpopulation of slowly cycling cells found in normal human skin.     

Development and homeostasis of the skin epidermis

The skin epidermis is a stratified epithelium that forms a barrier that protects animals from dehydration, mechanical stress, and infections. The epidermis encompasses different appendages, such as the hair follicle (HF), the sebaceous gland (SG), the sweat gland, and the touch dome, that are essential for thermoregulation, sensing the environment, and influencing social behavior. The epidermis undergoes a constant turnover and distinct stem cells (SCs) are responsible for the homeostasis of the different epidermal compartments. Deregulation of the signaling pathways controlling the balance between renewal and differentiation often leads to cancer formation.     

Bar synapses in the end buds of lamprey skin

Summary The end buds of lamprey epidermis have been considered to be similar to taste buds, but the synapses on the receptor cells are of the type with a dense mass surrounded by lucent vesicles, which is not found in gustatory cells. It is suggested that the end buds may belong to the lateralis sensory system and be involved in the light sensitivity of lamprey skin.     

Designer skin: lineage commitment in postnatal epidermis

The epidermis is populated by stem cells that produce daughters that differentiate to form the interfollicular epidermis, hair follicles and sebaceous glands. Diffusible factors, cell-cell contact and extracellular matrix proteins are all important components of the microenvironment of individual stem cells and profoundly affect the differentiation pathways selected by their progeny. Here, we summarize what is known about stem-cell populations and lineage relationships within the epidermis. We also present evidence that postnatal epidermis can be reprogrammed, altering the number and location of cells that differentiate along specific epidermal lineages.     

Pattern formation in plant epidermis through inhibition of immediately adjacent cells by pattern elements

Summary Examples of short-range inhibition in plant development were sought which satisfy four criteria for simplicity of expression. The range of inhibition extends only to adjacent cells and these criteria are (1) pattern of expression is within a two-dimensional array of cells, (2) cells of the array do not proliferate during pattern formation, (3) spacing between special cells extends only for a distance of one cell, and (4) no unequal cell divisions occur to complicate the pattern of cell arrangement. In one case of hairs or trichomes, the cells are evenly dispersed over the adaxial surface of the sepal ofSalvia splendens L. The R value of Clark and Evans is 1.64 for hair arrangement and hairs are formed from 21.1% of the epidermal cells. Based on cell behavior and an assumed method of inhibition, ordinary differential equations were written for formation of three types of cells in the tissue, free cells (F), trichome-bearing cells (T), and inhibited cells (I). Computer generated numerical solutions for these equations give cell type frequencies of 0.056 (F), 0.198 (T), and 0.745 (I), close to the observed values of 0.057 (F), 0.211 (T), and 0.731 (I). A similar approach was employed in analysis for the deployment of the cotton fibers in the ovular epidermis ofGossypium hirsutum L. and for that of the floating stomata of the fernAnemia phyllitidis (L). Sw. In general, these three patterns of epidermal deriviatives are most easily explained by one-cell wide inhibition fields between inhibiting special cells and inhibited contiguous cells. Other patterns in plants cannot be explained by this mechanism.     

Langerhans cells are strongly reduced in the skin of transgenic mice overexpressing follistatin in the epidermis

Activins are members of the transforming growth factor-beta (TGF-beta) family and are important for skin morphogenesis and wound healing. TGF-beta1 is necessary for the population of the epidermis with Langerhans cells (LC). However, a role for activin in LC biology is not known. To address this question, we analyzed skin from transgenic mice overexpressing the activin antagonist follistatin in the epidermis. Using immunofluorescence, we observed a striking decrease in the number of LC in the epidermis of transgenic mice in comparison to wild-type mice. Nevertheless, these LC expressed normal levels of major histocompatibility complex (MHC)-class II and Langerin/ CD207 in situ. In explant cultures of whole ear skin the number of dendritic cells (DC), which migrated into the culture medium, was reduced. This reduction was even more pronounced in cultures of epidermal sheets. Virtually all emigrated cutaneous DC displayed typical morphology with cytoplasmic "veils", showed translocation of MHC-class II to the surface membrane, and expressed the maturation marker 2A1. Thus, cutaneous DC from transgenic mice seemed to mature normally. These results demonstrate that overexpression of follistatin in the epidermis affects LC trafficking but not maturation and suggest a novel role of the follistatin-binding partner activin in LC biology.     

Reconstructed human epidermis for skin absorption testing: results of the German prevalidation study

Exposure to chemicals absorbed by the skin can threaten human health. In order to standardise the predictive testing of percutaneous absorption for regulatory purposes, the OECD adopted guideline 428, which describes methods for assessing absorption by using human and animal skin. In this study, a protocol based on the OECD principles was developed and prevalidated by using reconstructed human epidermis (RHE). The permeation of the OECD standard compounds, caffeine and testosterone, through commercially available RHE models was compared to that of human epidermis and animal skin. In comparison to human epidermis, the permeation of the chemicals was overestimated when using RHE. The following ranking of the permeation coefficients for testosterone was obtained: SkinEthic > EpiDerm, EPISKIN > human epidermis, bovine udder skin, pig skin. The ranking for caffeine was: SkinEthic, EPISKIN > bovine udder skin, EpiDerm, pig skin, human epidermis. The inter-laboratory and intra-laboratory reproducibility was good. Long and variable lag times, which are a matter of concern when using human and pig skin, did not occur with RHE. Due to the successful transfer of the protocol, it is now in the validation process.     

Vertebrate skin type I collagen: comparison of bony fishes with lamprey and calf

1. Characterization of Type I collagen alpha chains, alpha 1 and alpha 2, in the skin tissues of carp and common mackerel revealed a marked interspecies difference in CNBr-peptide maps of the alpha 2 chains, suggesting the hypervariability during evolution of the alpha 2 chains relative to the alpha 1 chains. 2. When compared with calf Type I collagen, lower vertebrate Type I collagens derived from these bony fishes as well as from lamprey were found to exhibit a higher degree of structural similarity between their alpha 1 and alpha 2 chains.     

Gap junctions in the cardiac muscle cells of the lamprey

Summary Electron microscopy of both thin sections and freeze-fracture replicas has demonstrated the occurrence of gap junctions (nexuses) in the cardiac muscle cells of the lamprey. These gap junctions are identical in basic structure with those found in the mammalian heart. However, they are much smaller (less than 0.5 in diameter), and more irregularly distributed than the typical gap junction in the mammalian heart. These small gap junctions seem to provide a structural basis for the electrical coupling between cardiac muscle cells in the lower vertebrates.In addition, the well developed sarcoplasmic reticulum and subsurface cisternae, which contain an electron dense spheroidal cast, are frequently observed in the cardiac muscles of the lamprey.This work is supported by a research grant from the Ministry of Education, Japan